BERKELEY, CA (UroToday.com) - Molecular imaging by means of positron emission tomography (PET) provides a method to study metabolic activity of tumors in vivo.
18F- or 11C-choline, occasionally called 18F- or 11C -acetate, are used as tracers for prostate cancer, reflecting the phospholipid metabolism. The hybrid technology PET/CT reduces image fusion mismatches significantly. Several studies have compared PET results with histological specimens for primary or recurrent prostate cancer. For primary diagnosis and staging, the majority of studies reported a specificity and positive predictive value between 80 and 90%. Sensitivity and negative predictive value are often slightly lower as particularly small cancer volumes cannot be detected by any imaging method in oncology.
Local prostate cancer recurrence after primary radiation treatment usually originates in the location of the primary tumor. Focusing the dose escalation on the actual tumor is an option to increase tumor control without increasing toxicity. Treatment planning for prostate cancer with a PET/CT-defined, simultaneous, integrated boost allows an individually adapted dose escalation and improves the therapeutic ratio considerably. Image-guided radiotherapy (IGRT) and intensity-modulated radiotherapy (IMRT) are prerequisite technologies for applying the simultaneous-boost concept. Boost techniques are applied as a standard in all radiotherapy departments for many cancer sites.
We could demonstrate a considerable improvement of the therapeutic ratio in a treatment-planning study using 18F-choline PET/CT, showing the possibility of a considerable dosage escalation to the macroscopic tumor, with only minor changes of the dosage to the rectum and bladder. No significant changes of the normal tissue complication probability (NTCP) was found for the organs at risk, so that toxicity will most likely not increase despite considerably larger doses to the tumor. The PET/CT-defined tumor volume and standard uptake value (SUV) levels correlate with several well-established prognostic risk factors, in particular a Gleason score >7, so that dose escalation in larger volumes can be limited for more aggressive, primary tumors.
Radiotherapy is the only curative treatment option for a recurrence after radical prostatectomy. Dosage escalation is a useful option in case of a local or locoregional recurrence, as increasing doses has been associated with increased biochemical control rates. Focusing the dosage escalation on the region of recurrence is, again, an option to increase effectiveness without increasing toxicity. For patients with recurrent prostate cancer after radical prostatectomy and a PSA >1 to 2 ng/ml, or a short PSA doubling time, PET/CT is an ideal imaging method before deciding the usefulness of local salvage radiotherapy (the only curative treatment option) and for treatment planning.
Clinical results are needed in the near future to support the effectiveness of these concepts.
Written by:
Micheal Pinkawa, MD., Et Al., as part of Beyond the Abstract on UroToday.com. This initiative offers a method of publishing for the professional urology community. Authors are given an opportunity to expand on the circumstances, limitations etc... of their research by referencing the published abstract.
PET and PET/CT in radiation treatment planning for prostate cancer - Abstract
